"Smart Gun"(?) ideas:

Fingerprint recognition? Two different toaster-oven sized fingerprint readers could not read my fingerprints when I was applying for my license to carry, so that technology is a no-go as far as I'm concerned. And don't wear gloves.

RFID "keyless ignition"? Potentially hackable or jammable.

Voiceprint recognition? Does your voice change under stress, and will your trigger's Siri recognize it if it does?

DNA recognition? Grip sensors have to read your DNA before you can fire. Just be sure to wipe off your grip before the bad guy gets possession of the gun. And don't wear gloves.

Eyeprint recognition? Take off your sunglasses or eyeglasses, hold your gun up to your eye, then shoot.

Thought recognition? Quick, think of your unique password!

Aura recognition? (Insert Twilight Zone theme here.)

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What, me worry?